This invention relates to a method for cementing a well and to apparatus useful in well cementing operations.
In the conventional drilling of a well, such as an oil well, a series of casings and/or liners are commonly installed sequentially in the wellbore or borehole. In standard practice, each succeeding liner placed in the wellbore has an outside diameter significantly reduced in size when compared to the casing or liner previously installed. Commonly, after the installation of each casing or liner, cement slurry is pumped downhole and back up into the space or annulus between the casing or liner and the wall of the wellbore, in an amount sufficient to fill the space. The cement slurry, upon setting, stabilizes the casing or liner in the wellbore, prevents fluid exchange between or among formation layers through which the wellbore passes, and prevents gas from rising up the wellbore.
The use of a series of liners which have sequentially reduced diameters is derived from long experience and is aimed at avoiding problems at the time of insertion of casing or liner installation in the wellbore. The number of liners or casings required to reach a given target location is determined principally by the properties of the formations penetrated and by the pressures of the fluids contained in the formations. If the driller encounters an extended series of high pressure/low pressure configurations, the number of liners required under such circumstances may be such that the well cannot usefully be completed because of the continued reduction of the liner diameters required. Again, a further problem of the standard well liner configuration is that large volumes of cuttings are produced initially, and heavy logistics are required during early phases of drilling.
While several approaches to the resolution of these problems have been attempted, none have proven totally satisfactory. Accordingly, there has existed a need for a well lining and cementing technique or procedure, and means to carry it out, which would eliminate or significantly reduce the degree of diameter reduction required when a series of well liners must be inserted. The invention addresses this need.
There is thus provided, in one embodiment, a method or process, useful in cementing a well, especially a hydrocarbon well, which is characterized by the use of increased external and internal diameter liners, i.e., by a reduction in the degree of diameter reduction of the liners required, and which does not require excessively large initial conductor casing or surface pipe. Accordingly, in this embodiment, the invention relates to a method of cementing a wellbore in which a casing or first liner is provided in a wellbore. (As utilized herein, the terms xe2x80x9cfirstxe2x80x9d and xe2x80x9csecondxe2x80x9d, etc., in relation to the casing or liners mentioned, are relative, it being understood that, after the initial xe2x80x9csecondxe2x80x9d casing or liner is cemented, it may become a xe2x80x9cfirstxe2x80x9d liner for the next cementing operation as such operations proceed down the wellbore.)
Further drilling operations are then conducted to provide an enlarged wellbore. As used herein, the term xe2x80x9cenlarged wellborexe2x80x9d refers to a wellbore or borehole having a diameter greater than that of the internal diameter of the casing or preceding liner, preferably greater than the external diameter of the casing or preceding liner, such a wellbore being provided or drilled in a manner known to those skilled in the art, as described more fully hereinafter. At a desired depth, or when it is otherwise decided to line and cement the enlarged wellbore, a second liner, whose greatest external (outside) diameter approximates, i.e., is only slightly smaller than the internal diameter of the casing or first liner provided, is then provided in the enlarged wellbore through the casing or first liner. The second liner comprises a minor section or segment of significantly or further reduced external and internal diameter (in relation to the remaining or remainder segment of the second liner) and is composed, at least in said minor section, of a deformable liner material. According to the invention, the second liner is positioned in relation to the enlarged wellbore so that the section of reduced external diameter is located or positioned in the lower portion of the casing or first liner and the remainder segment below the lower portion, in such manner that fluid may circulate freely, i.e., without substantial or significant impediment, in the annuli formed by the second liner and the enlarged wellbore and the internal wall of the casing or first liner.
Inside the bore of the larger remaining or remainder segment of the second liner there is disposed or provided, as more fully described hereinafter, a movable, fluid tight die member of appropriate dimensions, preferably positioned in the second liner distant from the bottom of the remainder segment and proximate the minor section of reduced external and internal diameter, and which, after initial positioning or installation in the enlarged wellbore, is fixed in relation to said wellbore. As utilized herein, the phrase xe2x80x9cfluid tightxe2x80x9d, in reference to the die member, is understood to indicate that the die member is appropriately sized and shaped and contains appropriate sealing means to prevent significant passage of fluid, even under substantial pressure, as described hereinafter, past its periphery or circumference which is contiguous to the interior wall or bore of the remainder segment of the second liner. The fluid tight die member, including the sealing means, is further a component or element of the novel die-expansion assembly of the invention which comprises means for transmitting a fluid to the bore of a liner, and means for connecting the die member to a drillstring. The latter means are important in positioning the novel liner-die assembly in the enlarged wellbore initially, as described more fully hereinafter, and in responding to applied fluid pressure. As utilized herein, the term xe2x80x9cdrillstringxe2x80x9d is understood to include tool members or collars, etc., normally utilized in wellbore operations. In the specific context of the invention, the die-expansion assembly comprises means for transmitting a fluid to the bore of the remainder segment of the second liner, to the end that a fluid under significant pressure may be applied to the bore of the remainder segment of the second liner, and further comprises means for connecting the die member to a drillstring.
According to the method of the invention, upon proper positioning of the liner-die assembly of the invention in the wellbore, cement slurry is then pumped down the drillstring through the casing or first liner and the second liner (via the means for transmitting a fluid) and into the enlarged wellbore annulus in an amount sufficient to cement the wellbore annulus. After the cement is in place, the bottom or bottom end of the second liner is sealed, by standard techniques known to those skilled in the art, to prevent egress of fluid from the liner. As utilized herein, reference to the xe2x80x9cbottomxe2x80x9d or xe2x80x9cbottom endxe2x80x9d of the liner is to be construed as referring to a site downhole on or in the liner rather than as a precise location of the liner body. The sealing of the bottom end of the liner, coupled with the seal provided by the fluid tight die member, provides or constitutes, assuming a location of the die member removed or distant from the bottom of the liner, and, with the exception of communication with the aforementioned means for transmitting a fluid, a sealed compartment or recess in the bore of the remainder segment of the second liner. Substantial fluid pressure is then applied to the interior of this sealed remainder segment recess by pumping a fluid, e.g., a wellbore fluid such as a drilling fluid or a spacer fluid, through said means for transmitting a fluid which communicates with the compartment or recess. As fluid under pressure is introduced into the otherwise sealed recess, the increasing pressure therein tends to force the fluid tight die member up the second liner bore. According to the invention, as fluid pressure is increased in the sealed recess, the position of the die-expansion assembly, including the die member, is mechanically adjusted or allowed to adjust by translation upward in the liner (and the wellbore). The rate of upward adjustment or movement of the die-expansion assembly by upward movement of the running string and the application of pressure to the second liner bore recess are correlated so as to produce movement of the die member up through the section of reduced diameter with concurrent gradual deformation and expansion of the section of reduced diameter, providing an expanded section or segment having an external diameter equal to or approximating, preferably slightly greater or larger than that of the remainder segment of the second liner, as described more fully hereinafter. The expansion of the section provides an external diameter for the section which more closely approximates the internal diameter of the casing or first liner, while providing a larger flow passage internally for production fluids. Continued application of fluid pressure and correlated upward translation or adjustment of the position of the die-expansion assembly frees the die member from the second liner, the second liner then being positioned or allowed to remain with a substantial minor portion of the newly expanded segment in the casing or first liner. The cement slurry in the wellbore annulus is then allowed to set.
In yet further embodiments, the invention relates to a novel liner, which may additionally include expansion means therein; to an apparatus or tool for expansion of a liner having a reduced diameter section; and to a novel liner-die assembly or combination which is useful in cementing operations. More particularly, the liner of the invention comprises a wellbore liner having a minor section of reduced external and internal diameter composed of a deformable material and a larger remainder section of increased external and internal diameter. The expansion device or apparatus of the invention comprises unique fluid tight die means adapted for expansion of a liner section of reduced internal and external diameter, and preferably comprises a means for transmitting a fluid, e.g., a pipe; a die member adapted for expanding, at least substantially uniformly, the bore of a liner, on the periphery of said pipe; and sealing means positioned on the periphery of the die member adapted to provide a fluid tight seal between the bore of a liner and said die member. In the preferred arrangement, the pipe is provided at one end thereof with means for connecting the pipe to, or for suspending the pipe from, a drillstring, and is further preferably provided at the opposite end thereof with means for suspending a tool, preferably components used in cementing operations, and, especially, in one aspect of the invention, means to assist in sealing the end of the liner distant from said opposite end of the pipe.
The invention further relates to a novel liner-die assembly. In this aspect, the invention comprises the novel wellbore liner in which there is disposed the die-expansion assembly of the invention, as described, the assembly being disposed in said liner with the longitudinal axis of the means for transmitting fluid, or pipe, coincident with the axis of the liner and the fluid tight die member positioned in the remainder segment of the liner.